Various technical applications involve power switches intended to act as an open circuit or a closed circuit according to a control voltage, with the capability of handling currents of the order of, e.g., 1 to 10 A.
These switches are expected to be able to operate indifferently with currents flowing through the switch in either direction, possibly with floating terminals which, unlike conventional HSD and LSD arrangements, may not comprise terminals connected to ground or a positive supply rail.
So-called SIMO (Single Inductor Multiple Load) arrangements where n loads are supplied sequentially by using n power switches with floating terminals are exemplary of a possible use of these switches.
Another possible field of application is with resonance converters, where switches play the role of auxiliary switches for the resonating circuit.
Circuits comprising transistors, e.g., metal-oxide semiconductor (MOS) transistors in an anti-series (back-to-back) arrangement are often used, possibly with mutually-connected source terminals, with the capability of driving the respective gates with a single control signal.
Two (MOS) transistors may be used in that case insofar as the diodes between the drain and the source terminals would prevent switching to an open (non-conductive) state in a polarization condition, that is when the diode is in direct (forward) conduction.
Such an arrangement has the advantage of a reduced DC power dissipation insofar as the drop across the switch is given by the sum of the “on” resistances Rds(on) of the two transistors.
In certain applications, especially when high switching frequencies come into play, acting on the gate of just one of the two transistors (that is, using the other transistor in the pair as a diode) may be advantageous: even if conduction losses may be higher, the voltage drop related to Rds(on) is generally lower than the voltage drop related to a diode in direct (forward) conduction.
Oftentimes, when reverse polarization is applied to a MOS transistor, using the intrinsic diodes between drain and source may be advantageous.
In the case of MOS transistors with a high BVdss (e.g., higher than 20 V) the rapid shutdown of these diodes when in operation may lead to an appreciable extra-current caused by the charge stored, a phenomenon known as “reverse recovery current” of the body-source diode of the switch in direct conduction.
Especially in high-frequency switching systems, this phenomenon may limit performance or even possibly prevent satisfactory operation.
By referring (just by way of example) to switches comprising solid-state components manufactured with a BCD (Bipolar-CMOS-DMOS) process, in the presence of a current to be switched of the order of, e.g., 1 A, the extra current peak may be as a high as 10 A with corresponding Vds voltages of the order of 10 V, which leads to (very) high power dissipation.